There are several studies where vitamin D works (amazingly well), and one study where it does not. But in the study where it does not work, it's an oral supple

There are several studies where vitamin D works (amazingly well), and one study where it does not. But in the study where it does not work, it's an oral supplement given after hospitalization. Oral vitamin D takes a while to elevate blood levels so the fact that such regimen doesn't work, doesn't prove much.